1. Field of the Invention
The invention relates to the field of manufacturing nanometer probe tips, and in particular, to probe tips having sensor structures and holes defined at the tip of the probe of the order of a few nanometers for use in atomic force microscopy, scanning tunnel microscopy, near field optical sensing and related scanning technologies.
2. Description of the Prior Art
Atomic force microscopes, scanning tunneling microscopes, near field optical probes and similar nanometer type probes utilize a small, sharp needle-like probe, which is brought into close proximity with the sample surface under controlled conditions. The probe tip is sharp and is of the order of nanometers. While controlling the physical interaction between the probe tip and the scan surface, the sample is scanned by the probe, typically by moving the sample with a piezoelectric controlled stage. Deflections in the probe are typically measured through optical beam methods, namely by the deflection of an optical beam reflected off a lever to which the probe tip is attached or which is an integral part of the probe and tip. Very small movements in the beam caused by a sample-to-tip interaction are thus translated optically into distinguishable optical and electronic signals. Movement of the piezoelectric stage on which the sample is mounted is combined in a graphic computer to provide a two dimensional map of the sample-to-tip interaction, which is usually determined by one or more characteristics of the sample surface.
The interaction between the probe tip may be of any type imaginable and typically includes physical interactions which are electronic, electrostatic, mechanical, thermal, chemical, optical or magnetic in nature. Surface images containing the information regarding a particular interaction on the surface with the probe tip can be attained with an extremely high resolution. Nanometer resolution or resolution on the angstrom atomic scale are typically achieved.
Although it is desirable to image the surface using all conceivable physical interactions between the probe tip and surface, scanning probes typically are designed to utilize a single interaction, or at least are predominantly affected by a single physical interaction. Heretofore, it has been extremely difficult to build probes which have a design that can materially respond to two or more different types of physical interactions between the probe tip and sample.
Since most of the sample-to-tip interactions are near-field effects, such as in the case of electron tunneling used in scanning tunneling microscopy, it is important to be able to fabricate the sensor immediately at the end of the probe tip in order to be as close as possible to the proximity or near-field effect. In addition, the requirement for spatial resolution for scanning microscopy is typically in the nanometer range. Therefore, the sensor size must be of the same order of magnitude, that is also in the nanometer range.
Prior art attempts to define sensor areas using microphotolithography has been extremely difficult even when using high frequency or high energy radiation. First, alignment of the photolithography masks to a few nanometers to locate the sensor exactly at the probe tip ranges from very difficult to impossible. Second, microphotolithography does not have the spatial resolution capable of making controllable patterns in the range below approximately 300 nanometers. While electron beam lithography can be used below the 300 nanometer limit, the deposition of photoresists on a needle-like, nonplanar probe tip is difficult, if not impossible, because of the difficulty in controlling the thickness of the mask layer. Repeatability of mask thickness is unattainable and yields are erratic. Therefore, what is needed is some type of nanofabrication process which is repeatable controllable to provide sensor sizes and locations without these defects.
Also what is needed is a method for fabricating a probe which can be used to respond to two or more physical interactions, and which will be able to locate the sensor at the very end of the probe tip and yet still define the sensing area to be only a few nanometers in size.